Method of testing telegraph transmission



Nov `19, 1929. H.INYQulsT 1,735,933

METHOD OF TESTING TELEGRAP-H TRANSMISSION Filed Jan. 20, 1928 .Bstorta'owv Set Ground www' S IN VEN TOR.

BY W

ATTORNEY Patented- Nov. 1e, 1929A r UNITED Estrarre H AnnY inrauisi,` or MILLBUiaN, -NEWJERSEL .AssIGNoR To AMEnicAN TELEPHONE e AND TELnGRArn-'coi/LPANX, n conPonATioN orNnW `Yom:

METHOD or TESTING' TELE-GRAPH lTRANS'Mission` Applicationfrileagnnuawvzo, 1.928. serial No. 248,100. Y

'AThis invention 'relates `to"itelegfraph sys-V tems and imore .particularly ito, improvements in .methods-of .and :means for :measuring tele-'- graph transmission by ,employing adistorted y 5 signals rather `than perfect signals.V

` Informer methods of Vmeasuring telegraph transmission, lwhich have Abeen utilfized, sof called";periect signalsxare usually employed at thesendingfend of :the circuit ,and the 1,0 vleiigtliening or shortening of these signals due to imperfections oi the :circuit is measured 'at the receiving Lend. These measurements are sometimes made :at fseveral speeds, and, 1n

addition, a `measurement may be made Witha` @1 5 speed-of-ailure meter, A fairly 'complete picture 'ont the quality of transmission adorded tby the .circuit may f be obtained by such methods. However, it has been dound that vsuchfa procedure fis somewhat complicated ttor .230 .use in connection. With field transmission maintenance, and Aaecor-.dingly., the primary object yoi the present invention is to provide a muiohsimpler procedureior measuring telegraph transmission which involves lmeasurej- :512,5 ments at only a single speed such as :the =norpossible Lto provide suitable lcircuits for intro# 'ducingeither 1bia.s,'characteristio or fontuitous components or any combination'oi1 xt-bese finto thefsignals to produoethe type of distorted signa'lfdesired. 'Hovvfeven .vi-t, is probably more convenient to measure and' to 'control :bias -th an eithfer oit theother two components.- Also, bias isa common .cause of poor transmission and-is fcomparatively easy' t0,y oorirect-tor in the'tieldoperation-.ofY telegraph circuits. khe? Y '-cordingly, in fthe Vt'estirrg"rnejthodf and arranyggge ments yof this invent-ion, bias isgin-troduced in? to thesignfalsto produce the vdesired distorted- .type of signal util-ized.. However, the siggnl maybefdistortedbypther WVith reterence to the idisitorted'srg'nals uti-` -is pointed outthat-wvith this inventio-n it is The telegraph jtransmission Vmeasuring i Y meth'odoi the present invention in Which disk torted signals are'used, involves introducing distortion into fthe signals either in 'preedeterf mined :amounts .orin fgradually increasing amounts. and measuring the "e'lect thereof 'at a recording'device, suchas a distortion measuringset, .at .the receiver; This method' rhas 1 `V an .advantage over methods involving "the ruse of undistorted signals *1n that 4it 'aor-dssa direct indication Vott the margin in transmis sion, i ze., lof the `ability oi the. circuit `tohandie :distorted signals "(so las to determine thekk 'amountfoi distortion which may be iadd'ed to thereceivedfsignaflsfbefore ithe Ytotal idistortion becomes excessive).

In 'the method-:oi this invention fthe .distori tion may y-be` impressed aft the :receiving -end of the 'circuit in 'order to determine the mar-V ginat thelrfec'eiving end. In .other Words the measurementof smargin "by impressing distortion on the .srgnalslat the receiving iendwill afford ,anidea ofthe permissible variation'in the circuit. The testingVV method roi fthe in'- vention imakes lit readily vipossible'to ascertain l 'how inauchdistortion may-tbe introduced lin the signalsv during transmission over the .cir-

euit before.=the Ireceiving lapparatuswilliiail i to .properly function. vThe inventionl may be more fullyunder.- stood from.. thev follfowingmdesoription, to-

gether with itheaccompany'ing drawing, 'in

gramfoi a .telegraphisystemto which' the 'testL arte applicable.`

[Inrthedravvinggis shown ya, transmission Eline Y i' `L finterconnectlngfa transmitting and receive` Ji'andJ. .A telegraphprinter 'sendingfdise `:trilm'itor may ;be.fconne cted to jack vJax-anchga f in@r :method `-Aand apparatus of .invention sourceV oi reversals may be connec'tedto jack y' J4. These j-,aelrsgarercormeeted.tothe foperaf't-V hielt of l ing winding 2 of a sending relayi- -Gonneetedivto Y resistance l6 and the jacks 5, J, and J7 to `which maybe connected, respectively, battery, ground, anda meter. `Connected in series lwith Winding 2 is-a retardation coil and a current limiting resistance. A condenser is bridged across the Winding 2Q lfhe actionof this inductance Yandvcondenser.isto round ofi 'the Wave shape of the signals through the lie-K.

i lay Winding When the circuit/is opened and fic `closedfby the` printer sending contacts which When rounded may be connectedto jack J 3.

Y oii'V signals are sentrthrough Winding 2, signals'with bias varying from about 66 per cent spacing to 66 percentmarking maybe ob- I tratedk areV particularly.,` useful in practice;

' Howevengany other ,desirable formofi tele-` graph-sending apparatusymight equally Well bequtilized `Withythe arrangements of vthis invention;` The line circuitL is connected to thew Windingrotza receiving relay 4. The con-r tactfof receivingfrelay 4- controls a circuit through the distortion'jmeasuring set-.5.. :The distortion measuring set 5 isivvell linownin the art and is morel completely:illustrated in Patent No. '1,628,392,5May 10i-,19277 ,toV S; I'

' Cory. Accordingly,v it is 'only illustrated in schematicr form herein rHoWeven.4 other `forms o-recording devicesesuch asa speed-ofailuremeter, a VWheatstone recorder, or. a

' printer mightbe used'with the methodv of 4thisinventionn ,The receiving relay 4 will-be provided Witha biasingwinding 7 f in series.y f Y ,with Which is avar'iable resistance 8, a meter -9, and abattery. 'Bychangingthevariable y resistance 8 anyjdesired amountof-bias mayl be introducedinto the signals at the receiving l "LWL Y The testing methodI of this invention, the

i purpose of which is .to vdetermine the margin at the receiving end-of the circ.uit,or, in other Words, to'determine hopwfmuch"distortion'may be vintroduced in the signals Vdurii'ig transmisf sion over the circuit beforetliereceiving station fwill fail toproperlyfunction, iszjas fol-` Y Ylows: `A source ,of-reversals, vor perfect signals, may `be connected to jack J rand these Y perfect-'signalsmaybe sent over the line L.

A leading .Will thenj-beitakien onthe'V 'distor- `tionmeasuring' lset V5; ".'This vvillpshow the -amountfof distortion `inherent in the r line it"- tortionwillrbe introduced into-perfect signals VVby transmission' Vover Ltheparticular `line 'in Y Vquestion., The variable 4resistance Smay then bey adJusted Y, toV Vintroduce i distortiony in ythe ormofbias i p Y f into thesignals atthe receiving end of' the *linef In accordance with the arrangements of this invention, the amount of distortion introduced in the form of bias in the signals may be gradually increased until lthe distortion measuring set 5 indicates that the maximum amount `01h-limit'V has been reachedl at Whichthe receiver will properly function. .Such maximumy amount -oilimit Will have been previously determined by exf f iperiment. The.: ,distortion measuring set 5 Willv indicate".theY per cent A, of distortion or bias in the'signals. For'purp'oses of illustrationletitfbe assumed-that it has been'deter- Will operatethe receiver, butwill not do so beyond this limit. Accordingly, j if the bias is gradually. 'increasedat the. receivincr'station until device 15 gives an indication-olisuch limit, then a reading of the bias introduced at such time Will give afy direct indicationpof `inst how much bias may fbeeintroduced in the signals before the receiver fails to operate, The limit for the amount of distortion -mined` by' experiment that With'() per cent' distortion, `as shown-by set-5, the signals Y maybe previously determinedby experiment as has been pointed out and1may differ for various types of signals. In other Words, the

4amount of distortion that manual signals might 'stand might be dierentfrom that in.

Vthe ease of printer signals. The testing method ymightalso beslightly varied byintroducing at the receiver arixedy andarbitraryiA amount of bias instead` of gradually.; increasing`H amounts. Upon ythe introduction .of :i a

i'ixed and known amouiitof'y bias a. reading Would b'eitaken on meter 5. Acomparisonof this reading with the known maximum limit in percent Would'malie it easilypossible to 7 ldetermine how much more or less thantthe iixed Aandfarbitrary.amount of bias might be introduced.- 1 y y While the invention hasbelen--disclosed in certain. specific arrangements whichy are Y deemed-desirable, .it isunderstood thatl itis capable `of embodiment .in manyv .and other Widely varied forms without departing from the spirit of the invention as Ldenedfby. thev appended claims?Y -r' l fr VVhatis claimed iszvl l l'!-1 .-']lie method ofi-testing transmission `in. Va telegraph4 circuit interconnectinga transmitting and a 'receivingVV station whichy comprises introducing.'distortion at the receiving i175 f t stationninto the signals received-thereat, meas- Y uring lthe distortionin' suchy signals, `and fcom- Y -paringthis measurement and the amount of distortionlintroducedlwith the! known maximum allowable distortion for such signals'.- 2." The kimethod. yof testing transmission in a telegraphlfcircuit interconnecting atransy jmittingI and' a Y receiving Vstation' which iconiprises introducing distortion at lthe receiving station into the `signals received' thereat,

Ameasuring `the distortion in such signals, and gradually increasing saidlfintroduced'rdistor- A tion until` said measurements indicate-the known maximum allowable distortion for such signals.

8. A telegraph testing system comprising a line circuit interconnecting a transmitting and receiving station, means at said transmitting station for sending perfectsignals i over said line, a receiving relay at said receiving station', an adjustable biasing circuit for said receiving relay, a circuit controlled by said relay, and a distortion measuring set in said circuit.`

In testimony whereof, I have Vsigned my name to this specification this 18th'day of January, `1928.

HARRY NYQUIST. 

